This invention relates in general to material handling equipments and has specific reference to an improved lift truck of the type comprising a load-carrying platform movable vertically under the control of a hoisting device comprising a mast mounted at the front end of the truck and supporting said platfrom.
This invention is concerned more particularly with a lift truck capable of meeting the requirements of safety regulations in force and of which the hoisting device cannot interfere with the stability, dimensional limits or mass of the truck.
It is known that a good truck stability is essential for improving its safety of operation and its performances in actual service, such as speed, acceleration and braking, while reducing to a large extent the load ascent and descent times.
Hitherto known lift trucks comprise as a rule a mast, whether fixed or hingedly mounted, disposed ahead of the front drive-wheel axle, this mast constituting the means for guiding a load-carrying platform adapted to receive tools such as forks, clamps or other specialized tools. Under the control of a hydraulic cylinder, the load can travel parallel to the mast.
This conventional structure leads to the construction of lift trucks supporting the load ahead of the front-drive axle, so that the steering rear axle must be ballasted in order to transfer the centre of gravity of the truck inside its polygonal basis of support. As a rule, this polygonal basis is an isosceles triangle of which the vertices constitute the projection on the ground of the vertical pivot axis of the steering axle and the points of contact between the drive wheels and the ground. Therefore, known trucks are relatively bulky and heavy, so that their operation is attended by a considerable power consumption. Furthermore, the position of the centre of gravity above the ground increases the risks of tipping the truck, for example when changing its direction of travel or applying the brakes. It is also clear that the increment in the truck mass, its distribution and the position of its centre of gravity develop vertical, transverse and longitudinal inertia forces, and consequently stray movements tending to endanger the operator's safety and the truck load.